Method of removing particles from a flexible support, and apparatus for practicing same

ABSTRACT

A method and apparatus for removing particles from a flexible sheet. The sheet is run over a rotating rod, rotating oppositely to the moment of the sheet. The rod is immersed on its lower side in a bath of solvent and excess solvent is removed from the bath and is filtered. Additionally, solvent may be applied to the sheet before it reaches the rotating rod or a negative pressure applied just upstream of the rod sucks away the particles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of removing particles such as foreignmatter and dust from a flexible support (hereinafter referred to merelyas "a support"), and an apparatus for practicing the method (hereinafterreferred to as "a dust removing apparatus").

2. Terminology

The term "support" as used ,herein is intended to mean a flexiblebelt-shaped article having a width of several centimeters to severalmeters, a length of more than several tens of meters, and a thickness ofseveral micrometers to several hundreds of micrometers. The belt-shapedarticle is made of a plastic film of polyethylene terephthalate,polyethylene-2, 6-napthalate, cellulose diacetate, cellulose triacetate,cellulose acetate propionate, polyvinyl chloride, polyvinylidenechloride, polycarbonate, polyimide or polyamide. Alternatively, thebelt-shaped article is paper coated or laminated with α-polyolefin suchas polyethylene, polypropylene or ethylene butane copolymer or is ametal foil of aluminum, copper or tin. The flexible belt-shaped productincludes one on which a preliminary manufactured layer is formed.

The support is coated with a coating solution such as a photo-sensitivecoating solution, a magnetic coating solution, a surface-protectingcoating solution, a charging-preventing coating solution, or a smoothingcoating solution, depending on its purpose of use. After the coatingsolution thus applied has been dried, the support is cut into pieceshaving a predetermined length and width. Typical examples of the productare photographic films, photographic papers, and magnetic tapes.

However, this terminology is by way of example only and is not intendedto limit the invention.

3. Background Art

In a conventional method of removing particles, such as foreign matteror dust from a support (hereinafter referred to as "a dust removingmethod"), a piece of unwoven cloth or blade suitably held is pushedagainst the support so that the particles are caught by the piece ofunwoven cloth or blade. In another conventional dust removing method, astream of clean air is applied to the support at high speed so that theparticles are separated from the support and led to a suction port.These methods are of dry type. On the other hand, a wet type dustremoving method has been known in the art in which the support isimmersed in a washing solution tank, in which the particles areseparated from the support by ultrasonic vibration. In anotherconventional wet type dust removing method, a washing solution isapplied to the support, and an air stream is applied to the support athigh speed and sucked therefrom (cf. Japanese Patent ApplicationPublication No. 13020/1974).

The above-described conventional dust removing methods still suffer fromseveral disadvantages.

For instance, in the method in which the particles are caught by theunwoven cloth or blade, the support may be scratched orelectrostatically charged by the friction, or the fibers of the unwovencloth may stick to the support.

The dust removing method using the high speed air stream is effective inremoving relatively large particles of several tens of micrometers ormore from the support. However, it is scarcely effective in catchingrelatively small particles or particles strongly adhering to thesupport.

In the wet type dust removing methods, the equipment is large in scale.Furthermore, in removing particles from the support running at highspeed, a large quantity of mist is produced which sticks to theperipheral devices and to the support from which the particles have beenremoved.

In order to eliminate the above-described difficulties the presentapplicant has proposed a dust removing method (Japanese PatentApplication (OPI) No. 150571/1984, the term "OPI" as used herein meaningan "unexamined published application"). In this method, as shown inFIGS. 1 and 2, a solvent is applied to the surface of a support 1. Whilethe solvent remains on the support 1, two stationary plates are pushedagainst the surface of the support 1 to remove the particles 18 togetherwith a part of the solvent from the support.

Thereafter, the inventor has conducted intensive research on a moreeffective dust removing method and an apparatus for practicing themethod, and accomplished the present invention.

SUMMARY OF THE INVENTION

In view of the above-described difficulties accompanying a conventionalmethod of removing particles such as foreign matter or dust from aflexible support, an object of this invention is to provide a method inwhich particles such as foreign matter and dust can be more effectivelyremoved from a flexible support. A further object is to provide anapparatus for practicing this method which is simple in construction.

The foregoing object and other objects of this invention have beenachieved by the provision of a method of removing particles from aflexible support in which, according to the invention, thesolvent-wetted surface of a rod member rotating in a direction oppositeto direction of running of the flexible support is set close to one sideof the flexible support so that the particles on the one side of thesupport are transferred onto the outer cylindrical surface of the rodmember, and separated from the outer cylindrical surface of the rodmember.

The invention further provides an apparatus for removing particles fromthe flexible support in which the solvent-wetted surface of the rodmember rotating in a direction opposite to the direction of running ofthe flexible support is set close to one side of the support so that theparticles on the one side of the support are transferred onto the outercylindrical surface of the rod member and separated from the outercylindrical surface of the rod member. According to the invention, theapparatus comprises a rod member connected to a rotating drive source soas to be rotated in a direction opposite to the direction of running ofthe flexible support and a block member having both a slit in which anegative pressure can be maintained and a slit into which a solvent canbe supplied. The block member is able to rotatably hold the rod member.Alternatively, instead of the negative pressure, solvent can be appliedto the support before it reaches the rod member.

It is preferable that the outside diameter of the rod member is in arange of from 1 mm to 50 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a part of a dust removingapparatus.

FIG. 2 is a sectional view showing a part of the apparatus in FIG. 1.

FIG. 3 is a sectional view, partly as a block diagram, showing a firstexample of a dust removing apparatus according to this invention.

FIG. 4 is a perspective view showing a part of the apparatus of FIG. 3.

FIG. 5 is an explanatory diagram outlining a coating apparatus used fordetermining the effect of the invention.

FIG. 6 is a sectional diagram, partly as a block diagram, showing asecond example of the dust removing apparatus according to theinvention.

FIG. 7 is a sectional diagram, partly as a block diagram, showing athird example of the dust removing apparatus according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be described with referenceto the accompanying drawings.

FIG. 3 is a sectional view showing a first example of an apparatus forremoving dust from a flexible support according to the invention, andFIG. 4 is a perspective view showing an operating state of theapparatus.

A flexible support 1 laid over a plurality of guide rollers 2 isconveyed in a predetermined direction in the direction of the arrow A.

A rod 3 is disposed between the aforementioned guide rollers 2 and 2 insuch a manner that it contacts the surface of the support 1 at a smalllap angle and is rotated at a considerably low speed in the direction Bopposite to the running direction A of the support 1. The peripheralspeed of the rod 3 is at least 0.1 cm/sec.

In order to rotate the rod 3, any drive source 4 may be employed if itcan provide a low speed rotation output. However, it is preferable toemploy an oil pressure motor or an air pressure motor for environmentsecurity against solvent gas.

In general, the rod 3 is 1 to 50 mm in diameter, and at least itssurface is composed of cemented carbide (such as WC-TAC) or fineceramics such as alumina A-150 or zirconia) and has a surface roughnessof 1 micrometers to 0.05 micrometer in R_(max). The length of the rod 3is longer than the width of the support 1.

The rod 3 is rotatably supported by a block 5 whose width issubstantially equal to the length of the rod 3.

The block 5 includes partitions 8, 9 and 10 which form slits 6 and 7 asshown in FIG. 3.

The upper ends of the partitions 9 and 10 are curved surfaces whoseradius of curvature is substantially equal to the radius of the rod 3 inorder to hold the rod 3. In the partition 10, a plurality of liquidoutlet holes 11 are formed at suitable intervals in such a manner thatthey are arranged horizontally near the top.

A liquid pool 13 is provided outside of the partition 10. In otherwords, the block 5 includes an outside wall 12 to form the liquid pool13 against the partition 10.

The slit 6 communicates through its bottom to an exhaust blower 14 sothat the air pressure in the slit 6 is maintained -20 to -100 mm-aq.,that is, a negative pressure relative to atmospheric pressure asmeasured in millimeters of water.

On the other hand, the slit 7 communicates with a solvent supplyingsystem consisting of a solvent supplying tank 15, a pressurizing pump 16and a filter 17, so that the slit 7 is filled with a solvent, such asxylole or butyl acetate. A larger part of the solvent flows through theliquid outlet holes 11 into the liquid pool 13, and is returned into thesolvent supplying tank 15 when necessary. Additional solvent is suppliedto the supplying tank 15 to compensate for solvent loss.

The apparatus thus constructed operates as follows.

The support 1 is run in the direction of the arrow A. When particles 18such as dust stuck to the surface of the support 1 approach the surfaceof the rod 3 rotating in the direction B opposite to the direction ofrunning of the support 1, they are separated from the surface of thesupport 1 by the rotation of the rod 3 and the air flow accompanying thesupport. As a result, the particles are transferred onto the surface ofthe rod 3, and are then delivered to the upper end of the slit 6 by therotation of the rod 3.

When the particles are delivered to the upper end of the slit 6, as wasdescribed above, most of the particles are separated from the surface ofthe rod 3 and sucked into the slit 6 by the negative pressure in theslit 6. The particles 18 thus sucked are discharged through the exhaustblower 14.

On the other hand, some of the particles 18 remaining on the surface ofthe rod 13 are separated form the rod 3 by the washing action of thesolvent supplied into the right-hand slit 7 while passing over the upperend of the slit 7. The particles thus separated are discharged throughthe liquid outlet holes 11.

The rod 3 covered with the solvent is continuously rotated, whichincreases the effect that the particles 18 are transferred onto thesurface of the rod 3.

In the lap region of the support 1 and the rod 3, a small gap is formedtherebetween by the air accompanying the support 1. The small gap thusformed permits the passage of fine particles. That is, it is difficultto completely remove the fine particles from the support because of thesmall gap thus formed. Therefore, it is desirable that a backing roll 19confronts the rod 3 with the support 1 therebetween, as indicated by thebroken line 19, as the case may be.

In the case where a number of particles 18 have adhered to the support1, they are liable to transfer onto one and the same part of the surfaceof the rod 3. If this is repeated, then the gap between the support andthe rod is locally increased to permit the passage of particles. Thatis, it becomes impossible to completely remove the particles from thesupport 1. In order to eliminate this difficulty, it is desirable toprovide means for reciprocally sliding at least the rod in the widthwisedirection of the support.

SPECIFIC EXAMPLE

The dust removing apparatus as shown in FIG. 3 using a xylole solventwas used to remove dust from one side of a support of polyethyleneterephthalate of 38 micrometer in thickness and 500 mm in width whichwas run at a speed of 200 m/min. After the dust was removed from thesupport, a coating apparatus 20, as shown in FIG. 5 and disclosed inJapanese Patent Application No. 94657/1984, was used to coat the oneside of the support 1 with the magnetic coating solution whosecomposition is indicated in the following Table 1. The support 1 wascoated by the magnetic coating solution to thicknesses of 3 micrometers,5 micrometers and 10 micrometers. The coated surface was then checkedfor pin holes and stripes.

The rod 3 of the dust removing apparatus was made of carbide (WC-TAC),and had a diameter of 6 mm and a surface roughness of 0.5 micrometer inR_(max). The rod was rotated at a peripheral speed of 0.5 cm/sec.

The pressure in the slit 6 was -60 mm-aq. and the flow rate of xylolesupplied to the slit 7 was 500 cc/min.

The magnetic coating solution was prepared as follows. The materialsshown in Table 1 were sufficiently mixed and dispersed in a ball mill,and mixed with epoxy resin (epoxy equivalent 500) of 30 parts by weight.The resultant mixture was further subjected to mixing and dispersing, toprepare the magnetic coating solution.

                  TABLE 1                                                         ______________________________________                                        γ-Fe.sub.2 O.sub.3 powder (needle-shaped                                                     300    parts by weight                                   particles having an average powder                                            diameter of 0.5 micrometer in the                                             major diameter direction; a coercive                                          force of 320 Oe)                                                              Vinyl chloride vinyl acetate                                                                       30     parts by weight                                   copolymer (copolymerization                                                   ratio 87:13, polymerization                                                   degree 400)                                                                   Electrically conductive carbon                                                                     20     parts by weight                                   Polyamide resin (amine value 300)                                                                  15     parts by weight                                   Recithin             6      parts by weight                                   Silicon oil (dimethyl polysiloxane)                                                                3      parts by weight                                   Xylole               300    parts by weight                                   Methyl isobutyl ketone                                                                             300    parts by weight                                   n--butanole          100    parts by weight                                   ______________________________________                                    

The results are as indicated in Table 2 below.

COMPARISON EXAMPLE

For a comparison, the magnetic coating solution was applied to thesupport under the same conditions as those of the above-describedspecific example except that the dust removing apparatus was not used.The coated surface of the comparison example was then checked for pinholes and stripes. The results are as indicated in Table 2 below:

                  TABLE 2                                                         ______________________________________                                                             Coated magnetic                                                  Dust removing      layer thickness                                            apparatus Defect   3 μm                                                                              5 μm                                                                            10 μm                               ______________________________________                                        Specific  Used        Stripes  0.2  0    0                                    example               Pin holes                                                                              0.6  0.2  0                                    Comparison                                                                              Not used    Stripes  10.2 6.5  4.8                                  example               Pin holes                                                                              85.1 41.3 35.3                                 ______________________________________                                         Note                                                                          In both the specific example and the comparison example, ten supports eac     of a length of 4000 m were used. The data in Table 2 indicate the numbers     of defects per support.                                                  

Now, a second embodiment of the invention will be described. Theembodiment provides a method of removing particles from a flexiblesupport, in which one side of the flexible support is coated with asolvent. A solvent-wetted surface of a rod member rotating in adirection opposite to the direction of running of the support is setclose to the one side of the support while the solvent also remains onthe support. As a result, the particles on the one side of the supportare transferred onto the outer cylindrical surface of the rod member andare then separated from the outer cylindrical surface of the rotatingrod member. The embodiment further provides an apparatus for practicingthe method.

A second example of the dust removing apparatus according to theinvention will be described with reference to FIG. 6. In FIG. 6, thosecomponents which have been previously described with reference to FIG. 3(the first example) are designated by the same reference numerals orcharacters.

As shown in FIG. 6, the apparatus has a block 5 having partitions 8, 9and 10 which form slits 6 and 7.

Liquid pools 13-1 and 13-2 are provided outside of the partitions 8 and10 on either side of the block 5. In other words, the block 5 includesoutside walls 12-1 and 12-2 to form the liquid pools 13-1 and 13-2against the outer partitions 8 and 10.

On the other hand, the slits 6 and 7 communicate with a solventsupplying system consisting of a solvent supplying tank 15, apressurizing pump 16 and a filter 17, and are filled with a solvent,such as xylole or butyl acetate. A larger part of the solvent isdischarged through the liquid outlet holes 11 into the liquid pools 13-1and 13-2. The solvent in the liquid pools 13-1 and 13-2 is returned intothe solvent supplying tank 15 when necessary.

In the apparatus thus constructed, the support 1 is run in the directionof the arrow A. When the particles 18 stuck to the surface of thesupport 1 approach the surface of the rod 3 rotating in the direction Bopposite to the direction of the arrow A, the particles are separatedfrom the surface of the support 1 by the rotation of the rod 3 and theaction of the solvent applied to the support 1 from the slit 6 and theparticles are transferred onto the surface of the rod 3. The particlesthus transferred are brought to the upper end of the slit 6 as the rod 3rotates.

On the other hand, the particles 18 transferred onto the surface of therod 3 as described above are separated from the surface of the rod 3 bythe washing action of the solvent supplied into the slits 6 and 7 whilethe solvent passes over the upper ends of the slits and 7. The particlesthus separated are discharged through the upper region of the slit 6 andthrough the liquid outlet holes 11.

The rod 3 covered with the solvent is continuously rotated, which actionfurther increases the effect that the particles 18 are transferred ontothe surface of the rod 3.

FIG. 7 shows a third example of the dust removing apparatus according tothe invention. In the apparatus, a solvent applying section (equivalentto the slit 6 of FIG. 6) is provided separately. That is, the solvent isapplied to the support by a roll coater 22. In FIG. 7, partscorresponding functionally to those already described with reference toFIG. 7 are therefore designated by the same reference numerals orcharacters.

SPECIFIC EXAMPLE

A convention roll coater was used to apply a xylole solvent to one sideof a polyethylene terephthalate support at a flow rate of 100 cc/m². Thesupport was 38 micrometers in thickness and 500 mm in width. While thesolvent remains on the support, the particles were removed therefromwith the dust removing apparatus of FIG. 7 using a xylole solvent.Thereafter, the coating apparatus 20 as shown in FIG. 5 was used toapply the magnetic coating solution to one side of the cleaned support 1to thickness of 3 micrometers, 5 micrometers and 10 micrometers. Thecoated surface was then checked for defects such as pin holes andstripes.

In the dust removing apparatus, the rod 3 was made of carbide (WC-TAC)and had a diameter of 6 mm and a surface roughness of 0.5 micrometer,and it was rotated at a peripheral speed of 0.5 cm/sec. The xylolesolvent was supplied to the slit 7 at a flow rate of 500 cc/min.

In the concrete example described above, the magnetic coating solutionindicated in Table 1 was used. The results are as indicated in Table 3below:

COMPARISON EXAMPLE

For a second comparison, the magnetic coating solution was applied tothe support under the same conditions as those of the second specificexample except that the solvent precoating operation and the dustremoving apparatus were not employed. The coated but uncleaned surfacewas checked for defects such as pin holes and stripes. The results areas shown in Table 3 below:

                  TABLE 3                                                         ______________________________________                                                             Coated magnetic                                                  Dust removing      layer thickness                                            apparatus Defect   3 μm                                                                              5 μm                                                                            10 μm                               ______________________________________                                        Specific  Used        Stripes  0    0    0                                    example               Pin holes                                                                              0.1  0.2  0                                    Comparison                                                                              Not used    Stripes  10.2 6.5  4.8                                  example               Pin holes                                                                              85.1 41.3 35.3                                 ______________________________________                                         Note                                                                          Both in the specific example and in the comparison example, ten supports      each 4000 m long were used. In Table 3, the numerical data are the number     of defects per support.                                                  

The invention provides many beneficial effects.

As was described above, the cylindrical surface of the rod 3 rotating inthe direction B opposite to the direction A of running of the support 1is brought into sliding contact with the surface of the support 1 fromwhich dust should be removed. As a result large air speeds are generatedin the atmosphere near the surface of the support. Therefore, the dust(particles) 18 floats from the surface of the support, thus beingeffectively transferred onto the surface of the rod 3.

A negative pressure is held in the slit 6 in the embodiment of FIG. 3.Therefore, the particles 18 transferred onto the surface of the rod 3are separated therefrom and discharged through the slit.

The solvent is supplied into the slit 7. Therefore, some of theparticles remaining on the surface of the rod are washed by the solventand discharged to the outside. At the same time, the surface of the rod3 is wetted with the solvent, and therefore the particles are moreeffectively transferred onto the surface of the rod 3. Thus, the dustcan be removed from the support with high efficiency.

In the second example of the dust removing apparatus shown in FIG. 6,the solvent is supplied into both of the slits, 6 and 7. Therefore, notonly are the particles 18 washed away from the surface of the rod 3 bythe solvent, but also the surface of the rod 3 is covered with thesolvent. Accordingly, the particles can be more effectively transferredonto the surface of the rod 3. That is, the particles can be removedfrom the support with high reliability.

What is claimed is:
 1. A cleaning method of removing foreign particlesfrom a flexible sheet, comprising the steps of:running a flexible sheetin a first direction adjacent a rod member, said rod member having anouter cylindrical surface; applying a solvent onto said flexible sheetupstream of said rod member; rotating said rod in a direction oppositeto said first direction, whereby particles on said flexible sheet aretransferred from substantially an entire width of said flexible sheet tosaid outer cylindrical surface; and separating said particles from saidouter cylindrical surface.
 2. A cleaning method as recited in claim 1,further comprising the step of wetting said outer cylindrical surface ofsaid rod with a solvent.
 3. A cleaning method as recited in claim 1,further comprising the step of applying a negative gas pressure to aside of said rod member from which said flexible sheet is run.